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Carbon and Graphite by Neal J. Johnson, National Carbon Co., Division of Union Carbide Corp., New York, N . Y . Demands for materials with special properties are being met through research and process improvements
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AND GRAPHITE now find increasingly wider use as materials of construction as size, density, and temperature limits are being pushed still higher by the exacting requirements of the space age. Control of raw materials and complex processing techniques have produced entirely new families of materials derived from existing carbon and graphite technology. Continuing work promises properties tailored to specific demands growing out of rapidly advancing process improvements. Among the newer carbon and graphite forms are:
0 recrystallized graphites having specific gravities in excess of 2.0 and approaching the theoretical maximum of 2.25 0 forms particularly well suited for applications requiring strength a t high temperatures and ultralow permeability 0 composites of phenolic plastics and graphite fabrics demonstrating unusual resistance to high-temperature combustion 0 felted forms of flexible carbon and graphite fibers which show promise as insulation and filter media for corrosive services 0 nuclear graphite of low permeability and extreme purity now being made in monolithic pieces 16 inches square and 20 feet long.
turing time, increasing size, and producing and evaluating such graphites. The shape and color of man-made diamonds, made by General Electric, can be controlled by varying the temperature of formation. Several carbonaceous raw materials are used, with high-purity graphite reported as the best ( 3 A ) . Graphite columns 30 feet long, 12 by 14 inches in cross-section, and weighing 3700 pounds, manufactured by National Carbon, make possible the increased application of the material in a variety of equipment calling for large-sized components. Interest continues in graphite single crystals and whiskers. Spry and Scherer have used a pulsed magnet to investigate the de Haas-van Alphen effect (4A), and Bacon has studied the growth, structure, and properties of graphite whiskers ( 7 A ) . A research program to investigate the friction mechanism of graphite uses whiskers as samples (ZA). A carbon arc-image furnace has been designed to grow single crystals of refractory compounds.
Properties
The influence of structural and chemical imperfections on the various properties of graphite were discussed in the first of a three-part article by Blackman (723). In another study, the effect of chemical treatment on the structure and properties of graphite was investigated (70B). The reactions of graphite with oxygen (2B) and the oxidation of carbon by N O have also been reported ( 7 7B). The specific heat of four graphites tested by Rasor and McClelland was close to the theoretical value of 0.52 B.t.u. per pound over the 3000" to 5500' F. range and then rose sharply to 1.0 B.t.u. per pound a t 6600" F. Thermal conductivity data up to 6600" F. fit the theoretical curve. The report describes a graphite helix electric resistance furnace used to reach the elevated temperatures (QB). A complete x-ray installation for the 100% radiographic inspection of graphite following physical and dimensional inspection has been described (8B). Other
Reported here are highlights of developments spanning approximately the 18-month period from mid-1 959 through late 1960. General The fund of knowledge and successful application experience with graphite as a high-temperature material of construction has led logically to a formalized research and development effort on advanced materials for missile and space vehicle components. As a part of this work, Wright Air Development Division of the U . S. Air Force's Air Research and Development Command announced the award of a three-year contract to National Carbon Co., Division of Union Carbide Corp., for work directed at developing radically improved grades of graphite for missile applications, reducing variation in mechanical and physical properties, reducing manufac-
Longest single piece of graphite for its cross-section is 30-foot column measuring 12 X 14 inches on sides. The 3700-pound giant typifies graphite stock required for new metallurgical processes under development in various U. S. industries VOL. 53,
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Intricate machining on 20-foot lengths of nuclear graphite-longest ever produced-includes boring 5.1 25-inch holes through full length. Tolerances for dimensions are =t0.005 inch
reports include an electron microscope study of graphite (4B) and materials and techniques for thermal transfer and accommodation ( 5 B ) . The properties and performance of pyrolytic graphite (6B) and a study of the variation with temperature of Young's modulus of polycrystalline graphite have been reported (7B). Comparison of the properties of various packing and sealing materials, including carbon-graphite, has been made (3B). A model for the structure of active carbon and a mechanism for its formation have been proposed by Wolff (72B); a mathematical treatment based on the model defines a structure consistent with available experimental data.
New Materials A high-density recrystallized graphite is being produced by a process that permits controlled variations in properties in any or all three crystal directions. Density as high as 135 pounds per cubic foot and room temperature flexural strengths of 6000 p.s.i. and more have been attained. Exceptionally low creep rate extends useful temperatures to approximately 5500' F. (3C). Phenolic-impregnated graphite fabrics, developed by Continental-Diamond Fibre Corp., show promise for missile and other applications requiring exceptional heat resistance. I n laboratory ablation tests, a 5000" F. oxyacetylene flame took more than 10 minutes to burn through a 0.25 inch thick samplea burn-through rate of less than 0.0005 inch per second. Metallic and ceramic coatings €or graphite continue to attract attention. Tungsten coatings applied by Linde Co.'s plasma arc torch show promise for
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protecting graphite rocket nozzles. Deposits of molybdenum carbonyl on a graphite substrate followed by a coating of aluminum-silicon eutectic are treated, and the graphite winds u p with coatings of MoSiz, and then of an alIoy of molybdenum. silicon, and aluminum, and finally an outer coating of alumina, according to 9ational Research Corp. The protective coating held up for 30 minutes at 3450' F. Siliconized silicon carbide coatings, by hfinnesota Mining and Mfg., as well as carbide. silicide. or metal-alloy coatings, by Vitro, are also being investigated.
Other combinations of refractory metals with graphite and metal- and ceramicbonded graphites have been reported by Linde, American Metal Products, Bendix, GE, Bell Aircraft, and Ford Motor Co. (ZC, 5C). Developments in pyrolytic graphite, produced through cracking of hydrocarbons, with carbon in the gas deposited on a conventional graphite surface, have aroused interest. This technique has been under study by GE Research. A premixed, thermosetting carbonaceous cement is available from Great Lakes Carbon Corp. in a range of consistencies and has a low curing temperature. A heating element has been made by impregnating glass cloth with colloidal graphite (7C). Carbon coating on steel for a n electron tube anode, under study by Texas Instruments Co., has an emissivity comparable to gas-carbonized nickel-clad steel with greatly reduced gas content. Graphite and carbon felts, kcith filament diameters of approximately 0.0003 inch, are proposed for insulation, gas filtration, and gasketing. I n neutral and reducing atmospheres, they can be used at temperatures up to 5000' F. (42). Impregnation of graphite with carbides of both titanium and silica, by Falls Industries, produces a material i.vith an extremely hard surface and low permeability. High-Temperature Technology A graphite tube furnace for testing interstitial compounds provided preliminary observations on methods of measuring mechanical properties at high
Hot and cold streams of corrosive chemicals used in manufacture of hydrogen peroxide interchange heat as they criss-cross through bank of impervious graphite heat exchangers at Becco Chemical Division, Food Machinery and Chemical Corp., Vancouver, Wash.
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temperatures (60). Techniques have also been described for high-temperature tensile and torsional testing of graphite up to 3000’ C . ( 2 0 ) . A carbon arc-image furnace consisting of two 60-inch paraboloidal mirrors provides a heating-rate range from 100 to 1000 B.t.u. per square foot-second for high temperature behavior studies of engineering materials (70). Studies based on 15 variously selected samples of graphite provide tensile and creep behavior at temperatures above 3000’ F. Analysis of the creep data was attempted in terms of three different creep equations ( 4 0 ) . Numerous studies of the properties of pyrolytic graphite have been made. Tensile strength u p to 2750’ C. was measured by Martens and Jaffee (5D), and Stover reported on the effects of annealing on the structure of pyrolytic graphite. His x-ray analysis revealed little initial crystalline order between layers and average layer separation about 2% greater than in graphite (80). The theory of thermal stresses has been extended to deal with problems involving graphite a t high temperatures ( 7 0 ) . Carbon arc lamps provide energy duplicating the solar constant, and solar simulators are being used to evaluate space vehicles equipment in terms of the conditions to be encountered outside the earth’s atmosphere (30). Applications
T h e first reported plant-scale data for comparing the Colburn and Hougen cooler-condenser design procedure with actual performance were taken on six 37-inch Karbate impervious graphite heat exchangers handling wet SO2 gas
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T h e application of heat exchangers in chemical plants, with attention to design, specification, and performance, was discussed (7E),as was a review of the engineering problems in using carbon and graphite as a material of construction in chemical plants (7E). Chlorophenol. Phenol is chlorinated in a n impervious graphite falling-film absorber by Reichhold Chemical Co. Water circulates on the shell side, cooling the film of organic material inside the vertical tubes. Simultaneous mass and heat transfer is accomplished in one unit, replacing a much larger glass-lined reactor (5E). Dichlorocyanuric Acid. Heat exchange between two corrosive process streams comprising essentially dilute HzS04 plus chlorinated organics is accomplished in graphite exchangers. Units handle substantial single “temperature cross,” in that cool streams leave a t exit temperatures considerably higher than thcise of the hot streams (4E). This is a development of Food Machinery
Largest diameter graphite combustion chamber ever built is this giant a t the Carteret, N. J., plant of American Agricultural Chemical Co., used to burn elemental phosphorus in air. Combustion chamber, with inner diameter of around 20 feet, consists of 320 accurately machined graphite blocks, each 9 X 22.5 X 36 inches. Tower a t left, also constructed of carbon blocks, is used for hydration step which produces phosphoric acid
and Chemical Corp., Mineral Products Division. Hydrochloric Acid. Some 40 tons a day of anhydrous HCl is produced by Diamond Alkali from 360/, hydrochloric acid using Karbate impervious graphite shell and tube reboilers serving the stripping columns. First unit went on stream in 1947, and tube replacement has been required only once in about every four years, with 24-hour-a-day operation (8E). Nine graphite exchangers are used by Eli Lilly as condensers recovering solvents iccluding ether, alcohol, acetone, acetic anhydride, acetic acid, chlorobenzene, benzene, and naphtha. Units handle HC1 a t strengths up to 3670 a t temperatures to 100’ C . ( 70E). Electrolysis converts troublesome waste HC1 to chloride for reuse in the process (ZE).
Hydrogen Peroxide. Heat generated in production of hydrogen peroxide is used in a bank of impervious graphite shell and tube heat exchangers to heat reactants entering system a t Becco Chemical Division of Food Machinery and Chemical Corp. Phosphorus and Phosphates. A test of pumps for circulation of corrosive and abrasive solutions used in applying phosphate protective coatings was made by Oakite Products, Inc. Impervious graphite pumps were well suited to the job ( 3 E ) . American Agricultural Chemical Co. installed the world’s largest graphite combustion chamber for burning elemental phosphorus in air. Subsequent hydration in a carbon tower produces H3P04. Tantalum Fluoride. A grid-type impervious graphite heat exchanger is used VOL. 53,
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of Construction Review (3A) J . Electrochem. Soc. 107, No. 10, 244c (1960). (4A) Spry, FV. J., Scherer, P. M., Bull Am. Phys. Soc. 4, 240 (1959). General Properties (1B) Blackman, L. C. F.: Research (London) 13, 390 (1960). (2B) Duval, X.. SOC.Chem. Phvs., Paris, June 1960. (3B) Fabian, R. J., Materials in Design Eng.50, N o . 7, 121 (1959). (4B) Hedley, J. A., Nature 188, 44 (1960). (5B) King, H. A., Intern. Symp. High Temp. Technol., Asilomar Conf. Grounds, Calif., 1959, p. 129. (6B) Lozier, W. W., Manofsky, M. F., Ceram. Age 75, No. 4>84 (1960). (7B) Mason, I. B., Knibbs, R. H., Nuture 188, hTo. 33 (1960). (8B) Nuclear Power 4, No. 37. 114 (1959). (9B) Rasor, N. S., McClelland, J. D., Wright Air Development Center Tech. Rept. WADC-TR 56-400, 1957. (10B) Ray, S., Indian J . Phys. 33? 282 (1959). (11B) Smith, R. N., Swinehart, J., Lesnini, D., J . Phys. Chem. 6 3 , 544 (1959). (12B) Wolff, W'. F., Zbid.,63, 653 (1959).
Biggest graphite cylinder ever m a d e measures 61 inches in diameter, is 72 inches long, a n d weighs 7 tons. Cylinder was cored to make sections for l a r g e tower
for concentrating and crystallizing ( 6 E ) . Zirconium. Zirconium is being reclaimed from waste salt cake by a redissolving process using HC1 and a grid-type impervious graphite heat exchanger made by Heil Process Equipment Corp. Nuclear Technology. Dzsigns or gascooled reactors have created demands for graphite of lower and lower permeability, and stock is also being produced with extremely high purity. Production techniques have been developed for nuclear grade graphite in pieces as long as 20 feet with a 16-inch square cross-section. h'umerous reports of technical work on nuclear graphite, not only as reactor structural material but f a fuel elements as well, have been published, but in both number and context are octside the scope of this review. Astronautics. Astronautical applications of graphite. including vario.Js graphite grades Ivith meiallic and ceramic coatings, continue to command interest. Impregnated graphite fabrics have been molded into missile components, and extensive development \I-ork is continuing. Metallurgy. I n the metallurgical field, corrosion-resistant refractories that can substitute for metals in selected applications have been studied, and graphite molds are being used for casting a wide range of hard-to-handle materials, including titanium and other reactive metals. Carbon linings for blast furnaces are finding greater acceptance than ever before, and continuous study of furnace
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performance and brick quality have resulted in improved lining life. Process Equipment Development
Concentric tube impervious graphite heat exchangers arranged in paired modtles have been developed. Two tube sizes and three tube lengths are offered ( 7 F ) . A high-temperature graphite tube furnace, introduced by Lindberg Engineering Co., capable of producing controlled temperatures from 1600 to 5000" F. was announced. For limited volume heating or cooling, a n exchanger in which parallel passages are drilled in a single piece of impervious graphite is available from Falls Indus. tries. Temperatures to 340' F. can be accommodated a t pressures to 75 p.s.i.g. A globe valve of impervious graphite featuring a seal of carbon and Teflon plastic to eliminate galling and sticking was introduced. Modular entrainment separators of impervious graphite provide effective separation of entrained liquids from corrosive gas streams. Both are National Carbon Co. products. Literature Cited General (1A) Bacon, R., J . A ~ p l . Phys. 31, 283 (1960). (2A) Bryant, P. J., Wright Air Development Division, Tech. Rept. WADD-TR60-529, May 1960.
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( I C ) Kunststof-Rundschau 5, No. 5, 257 (1960). (2C) Long, J. V., Wright Air Development Center Tech. Rept. WADC-TR 59-415, p. 48, 1959. (3C) Materials in Design Eng. 52, No. 5, 13 (1960). (4C) National Carbon Co., Division of Union Carbide Corp., New York, Bull. 104, November 1960. (5C) Taylor, K. M., Aiken, D. B., Wright Air Development Center Tech. Rept. WADC TR-59-415, pp. 44-7, 1959. High-Temperature Technology (1D) Gilbey, D. M., J . Less Common Metals 1, 139 (1959). (2D) Green, L., Stehsel, M. L., Waller, C. E., 115th Meeting, Electrochem. Soc., Philadelphia, Pa., May 1959. (3D) International Projectionist 35, No. 11, 164 (1960). (4D) Martens, H. L., Button, D. D., Sischbach, D. B., Calif. Inst. Tech., JPL Progr. Rept. 30-18, 1959. (5D) Martens, H. E., Jaffe, L. D.: J.AppZ. Phys. 31, 1122 (1960). (6D) Mordike, B. L., J . Less Common Metals 1, 132 (1959). (7D) Peters, R. W., Wilson, R. G., Wallio, M. A., Natl. Aeronautics Space Adm., TN D-505, October 1960. (8D) Stover, E. R., J . Metals 12, 721 (1960). Applications (1E) Buis, M., Corrosion Prevent. 3 Control ' 7, No. 3, 34 (1960). (2E) Chem. Eng. 67, No. 15, 63 (1960). (3E) Chem. Proc. 23, No. 7,. 66 (1960). (4E) Ibid.,No. 9, 120. (5E) Ibid.,22, No. 8, 42 (1959) (6E) Ibid.,p. 124. (7E) Gilmour, C. H., IND.END. CHEM. 52, 465 (1960). (8E) Meinhold, T. F., Draper, C. H., Chem. Proc. 23, No. 8 , 92 (1960). (9E) Revilock, J. F., Chem. Eng. 66, No. 1 9 , 77 (1959). (10E) Weyermuller, G., Lloyd, F. R., Chem. Proc. 22, No. 9, 44 (1959). Process Equipment Development
(1F) Chem. Eng. 66, No. 15, 171 (1959)
